Conventionally, there is a vehicle seat having a mechanism that is capable of instantaneously moving a headrest forwardly so as to support a head of a sitting person when a vehicle back-side collision happens. For example, Japanese Laid-Open Patent Publication No. 2002-142910 teaches a technique in which a support portion for supporting a head is moved forwardly from a headrest base portion using a four-joints link mechanism.
In this disclosure, the four-joints link mechanism is constructed of two parallel links that are disposed between the headrest base portion and the support portion. The two parallel links are retained in a postural condition in which the support portion is retracted toward the headrest base portion when the vehicle back-side collision does not yet happen. When the vehicle back-side collision happens, the condition is released. Upon release of the condition, the two parallel links is rotated so as to move the support portion forwardly by a biasing force.